Task.FromException 方法
定义
重载
| FromException(Exception) |
创建 Task,它在完成后出现指定的异常。Creates a Task that has completed with a specified exception. |
| FromException<TResult>(Exception) |
创建 Task<TResult>,它在完成后出现指定的异常。Creates a Task<TResult> that's completed with a specified exception. |
FromException(Exception)
public:
static System::Threading::Tasks::Task ^ FromException(Exception ^ exception);
public static System.Threading.Tasks.Task FromException (Exception exception);
static member FromException : Exception -> System.Threading.Tasks.Task
Public Shared Function FromException (exception As Exception) As Task
参数
- exception
- Exception
完成任务的异常。The exception with which to complete the task.
返回
出错的任务。The faulted task.
注解
此方法创建一个 Task 对象,该对象的 Status 属性为 Faulted ,其 Exception 属性包含 exception 。This method creates a Task object whose Status property is Faulted and whose Exception property contains exception. 当你立即知道任务执行的工作在执行更长的代码路径之前将引发异常时,通常使用方法。The method is commonly used when you immediately know that the work that a task performs will throw an exception before executing a longer code path. 有关示例,请参见 FromException<TResult>(Exception) 重载。For an example, see the FromException<TResult>(Exception) overload.
适用于
FromException<TResult>(Exception)
创建 Task<TResult>,它在完成后出现指定的异常。Creates a Task<TResult> that's completed with a specified exception.
public:
generic <typename TResult>
static System::Threading::Tasks::Task<TResult> ^ FromException(Exception ^ exception);
public static System.Threading.Tasks.Task<TResult> FromException<TResult> (Exception exception);
static member FromException : Exception -> System.Threading.Tasks.Task<'Result>
Public Shared Function FromException(Of TResult) (exception As Exception) As Task(Of TResult)
类型参数
- TResult
任务返回的结果的类型。The type of the result returned by the task.
参数
- exception
- Exception
完成任务的异常。The exception with which to complete the task.
返回
出错的任务。The faulted task.
示例
下面的示例是一个命令行实用工具,该实用工具计算每个目录中的文件中其名称作为命令行参数传递的字节数。The following example is a command-line utility that calculates the number of bytes in the files in each directory whose name is passed as a command-line argument. FileInfo FileInfo.Length 该示例只调用 FromException<TResult>(Exception) 方法来创建出错的任务(如果特定子目录不存在),而不是执行实例化对象并为目录中的每个文件检索其属性值的更长的代码路径。Rather than executing a longer code path that instantiates a FileInfo object and retrieves the value of its FileInfo.Length property for each file in the directory, the example simply calls the FromException<TResult>(Exception) method to create a faulted task if a particular subdirectory does not exist.
using System;
using System.Collections.Generic;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
public class Example
{
public static void Main()
{
string[] args = Environment.GetCommandLineArgs();
if (args.Length > 1) {
List<Task<long>> tasks = new List<Task<long>>();
for (int ctr = 1; ctr < args.Length; ctr++)
tasks.Add(GetFileLengthsAsync(args[ctr]));
try {
Task.WaitAll(tasks.ToArray());
}
// Ignore exceptions here.
catch (AggregateException) {}
for (int ctr = 0 ; ctr < tasks.Count; ctr++) {
if (tasks[ctr].Status == TaskStatus.Faulted)
Console.WriteLine("{0} does not exist", args[ctr + 1]);
else
Console.WriteLine("{0:N0} bytes in files in '{1}'",
tasks[ctr].Result, args[ctr + 1]);
}
}
else {
Console.WriteLine("Syntax error: Include one or more file paths.");
}
}
private static Task<long> GetFileLengthsAsync(string filePath)
{
if (! Directory.Exists(filePath)) {
return Task.FromException<long>(
new DirectoryNotFoundException("Invalid directory name."));
}
else {
string[] files = Directory.GetFiles(filePath);
if (files.Length == 0)
return Task.FromResult(0L);
else
return Task.Run( () => { long total = 0;
Parallel.ForEach(files, (fileName) => {
var fs = new FileStream(fileName, FileMode.Open,
FileAccess.Read, FileShare.ReadWrite,
256, true);
long length = fs.Length;
Interlocked.Add(ref total, length);
fs.Close(); } );
return total;
} );
}
}
}
// When launched with the following command line arguments:
// subdir . newsubdir
// the example displays output like the following:
// 0 bytes in files in 'subdir'
// 2,059 bytes in files in '.'
// newsubdir does not exist
Imports System.Collections.Generic
Imports System.IO
Imports System.Threading
Imports System.Threading.Tasks
Module Example
Public Sub Main()
Dim args() As String = Environment.GetCommandLineArgs()
If args.Length > 1 Then
Dim tasks As New List(Of Task(Of Long))
For ctr = 1 To args.Length - 1
tasks.Add(GetFileLengthsAsync(args(ctr)))
Next
Try
Task.WaitAll(tasks.ToArray())
' Ignore exceptions here.
Catch e As AggregateException
End Try
For ctr As Integer = 0 To tasks.Count - 1
If tasks(ctr).Status = TaskStatus.Faulted Then
Console.WriteLine("{0} does not exist", args(ctr + 1))
Else
Console.WriteLine("{0:N0} bytes in files in '{1}'",
tasks(ctr).Result, args(ctr + 1))
End If
Next
Else
Console.WriteLine("Syntax error: Include one or more file paths.")
End If
End Sub
Private Function GetFileLengthsAsync(filePath As String) As Task(Of Long)
If Not Directory.Exists(filePath) Then
Return Task.FromException(Of Long)(
New DirectoryNotFoundException("Invalid directory name."))
Else
Dim files As String() = Directory.GetFiles(filePath)
If files.Length = 0 Then
Return Task.FromResult(0L)
Else
Return Task.Run( Function()
Dim total As Long = 0
Dim lockObj As New Object
Parallel.ForEach(files, Sub(fileName)
Dim fs As New FileStream(fileName, FileMode.Open,
FileAccess.Read, FileShare.ReadWrite,
256, True)
Dim length As Long = fs.Length
Interlocked.Add(total, length)
fs.Close()
End Sub)
Return total
End Function )
End If
End If
End Function
End Module
' When launched with the following command line arguments:
' subdir . newsubdir
' the example displays output like the following:
' 0 bytes in files in 'subdir'
' 2,059 bytes in files in '.'
' newsubdir does not exist
注解
此方法创建一个 Task<TResult> 对象,该对象的 Status 属性为 Faulted ,其 Exception 属性包含 exception 。This method creates a Task<TResult> object whose Status property is Faulted and whose Exception property contains exception. 当你立即知道任务执行的工作在执行更长的代码路径之前将引发异常时,通常使用方法。The method is commonly used when you immediately know that the work that a task performs will throw an exception before executing a longer code path. 说明如示例所示。The example provides an illustration.